1. FIELD OF THE INVENTION
This invention relates to rock cutting teeth and more particularly to the replaceable tooth and tooth assembly used on a dredging cutterhead.
2. DESCRIPTION OF THE PRIOR ART
Dredge cutterheads are generally conical with a multiplicity of hard rock cutting teeth projecting outwardly from helical support vanes or blades disposed about the conical surface of the cutterhead. The cutterhead normally has a hub which fits around a shaft that provides the torque for turning the cutterhead in its operation of dredging the bottom of waterways. Because the cutterhead encounters rock which must be removed, the teeth on the cutterhead are made of hard materials with high impact properties, but this is not sufficient to prevent wearing and breakage of the teeth. Accordingly, it is highly desirable to provide a tooth design that has improved life and wearing capabilities and ease of replacement.
The most common variety of replaceable tooth for a dredge cutterhead embodies a pyramidal shape which is attached by an adapter to the cutterhead blade in a manner such that the point of the pyramid is directed at the surface which is to be cut and the longitudinal axis of the tooth, generally passes through the centroid of the cutter blade section and is generally at an angle with respect to the profile plane of the cutterhead from the point of the pyramidal tooth so as to provide an efficient transmission of power to the tooth with a minimum of breaking force.
It has been determined in actual practice that most failures of dredge cutterhead teeth and the supporting adapters occur from the outside to the inside due to high shock loads from a combination of severe dredging conditions involving the excavation of rock. The forces which are involved are produced by abrupt encounters with boulders, high swing loads, and radial shock loads involving "ladder bounce" even when ladder weights in excess of 500 tons have been employed. An analysis of these factors has led to the design of an entirely new tooth which significantly reduces the possibility of breaking due to externally applied forces. The bending moments in the tooth in accord with one embodiment of the present invention are reduced almost fifty percent (50%) over the present pyramidal design. Furthermore, the present invention includes a bifurcated tooth, in which one cutting arm is operational while the other cutting arm is nonoperational, but when sufficient wear of the operational arm has been experienced, the tooth can be removed from the adapter and rotated 180.degree. to bring the previously nonoperational cutting arm into the operational position while the arm with the worn cutting face or edge is placed in a nonoperational position. Thus, the tooth of the present invention has much longer useful life as compared to the prior art tooth. In accord with another embodiment of the present invention twice the wear life of the prior art tooth is obtained.
In accord with another embodiment of the invention the axis of the adapter and base of the tooth may be angled with respect to the axis of the adapter landing and the bifurcated teeth may be extended outwardly to the same radius of the normal single tooth cutting edge position, thus providing the approximate same length of tooth between the base and the cutting outer end portion as in the normal single tooth whereby approximately twice the life of the single point is achieved without increasing the torque requirements of the cutterhead, as would occur, if the bifurcated tooth were positioned on an adapter whose axis was aligned with its landing axis, with the axis of the base of the tooth also in alignment therewith.
A dredge cutterhead is shown by U.S. Pat. No. 3,808,716 and typical teeth for prior art dredge cutterheads are shown by U.S. Pat. No. 3,708,895 and by U.S. Pat. Nos. Des. 244,683 and 244,597. Other known U.S. Pat. Nos. are 640,622; 993,474; 3,544,166; and 4,098,013. Also there exist two Holland Patent Application Nos. 7808654 and 7808655, published on Mar. 8, 1979. Edge cutters for bucket excavators are also known with bifurcated teeth as shown in the November 1978 issue of "World Dredging and Marine Construction", page 30.
It is an object of this invention to provide a novel tooth for a dredging cutterhead. It is another object of this invention to provide a novel rock cutting tooth assembly for use in a dredging cutterhead. It is still another object of this invention to provide a novel bifurcated tooth for use in rock cutting operations in which only one tooth is operational unless rotated 180.degree.. A specific object is the provision of an extended wear life dredge cutter tooth. A particularly object is to provide a dredge cutter tooth which is more resistant to breakage from "ladder bounce" and other shock loads. Still other objects will appear from the more detailed description of this invention which follows.